The reaction of hydrocarbon feedstocks in the presence of catalysts to produce gasoline range products, diesel fuels, aromatics, or other valuable fuels and chemicals is frequently carried out using fixed catalyst beds at elevated temperature. These catalyst beds require periodic regeneration of the catalyst, commonly conducted by contacting the catalyst with an oxygen containing gas at elevated temperature in order to remove by combustion those coke and carbonaceous deposits responsible for the deactiviation of the catalyst. For continuous fixed bed catalytic processes, the process design generally incorporates at least two fixed bed catalyst reactors which are sequentially or alternately operated as a regenerator vessel or process vessel such that the catalyst is undergoing oxidative regeneration in one vessel while the alternate or "swing" vessel is converting the hydrocarbon feedstock to the desired product. In these processes provision is routinely made for the recirculation of the regeneration gas stream which requires recompression of the gas, makeup air compressor controls, filters and heat exchangers as needed to reconstitute the regenerator gas stream and recycle that stream under the precise conditions of temperature, pressure and composition needed to oxidatively remove the deleterious carbonaceous deposits on the catalyst. Examples of processes which use oxidative catalyst regeneration involving fixed bed swing reactors include reforming, catalytic hydrodesulfurization, catalytic dehydrogenation, the methanol-to-gasoline processes (MTG), and olefins upgrading such as the olefins-to-gasoline and distillate (MOGD) process, to name a few.
In order to facilitate the control of the composition of the gas, the flue gas generally used for regeneration is recycled. The prior art, such as U.S. Pat. No. 2,391,327 to Meckler, discloses processes for the regeneration of solid contact material used for promoting hydrocarbon conversion reactions using flue gas where the flue gas is generated in a regenerator gas combuster, recycled through heat exchange zones and filters and incorporates instrumentation to sense and adjust the composition of chemicals in the flue gas to the preferred ratios. The disclosure is illustrative of the complexities associated with the art of fixed bed catalyst regeneration using flue gas recycle and the degree of treatment and processing required for a recycle flue gas stream. Such treatment requires a significant investment in capital equipment and can be the source of inefficiencies in the overall process. Other examples in the prior art such as U.S. Pat. No. 2,278,509 to Brown and U.S. Pat. No. 2,215,868 to Bertetti are further illustrations in the prior art of inventions involving regeneration of solid catalysts using flue gas which is recycled. These inventions involving regenerator gas recycle are also faced with the problems noted heretofore of the requirement for substantial capital investment for heat exchange, recycle gas compression and chemical composition control in order to provide a recycle flue gas stream suitable for use in catalyst regeneration. The added costs and inefficiencies incurred in the course of providing a suitable recycle flue gas stream have represented a substantial problem and challenge to workers in the field of fixed bed catalyst regeneration.
It has been discovered that an available flue gas can be employed as the catalyst regenerating gas stream in a once through configuration consolidating flue gas and regenerating gas treatment steps. In particular, the process of this invention used available flue gas heat to preheat feedstock and oxidatively regenerate catalyst.
It is an object of the present invention to provide a process for the oxidative regeneration of catalysts employed in a fixed bed hydrocarbon conversion processes that is efficient and economically advantageous without requiring recycle of the regenerator gas stream.
It is another object of this invention to provide a process for the regeneration of fixed bed catalytic hydrocarbon conversion processes by combining available flue gas streams with catalyst regeneration in an efficient and economically advantageous configuration.
Yet another object of the present invention is to combine the catalyst regeneration of fixed bed hydrocarbon conversion processes with the catalyst regenerator operations of a fluid catalytic cracking process in a manner so as to achieve maximum utilization of commonly useful equipment and the energy resources in the FCC catalyst regenerator flue gas stream.